Thrust sliding bearing

ABSTRACT

A thrust sliding bearing  1  includes: a synthetic resin-made upper casing  3  which has a vehicle body-side seat surface  10  for a mounting member  8  on a vehicle body side and an annular lower surface  2;  a synthetic resin-made lower casing  5  on which an annular upper surface  4  opposed to the annular lower surface  2  and a spring seat surface  25  for a suspension coil spring  7  are integrally formed, and which is superposed on the upper casing  3  so as to be rotatable about an axis O of the upper casing  3  in an R direction; and a synthetic resin-made thrust sliding bearing piece  6  which is disposed in an annular gap  9  between the annular lower surface  2  and the annular upper surface  4,  and has an annular thrust sliding bearing surface  51  which slidably abuts against at least one of the annular lower surface  2  and the annular upper surface  4.

This application is a divisional of application Ser. No. 12/936,008filed Oct. 1, 2010, which in turn is a national phase of InternationalApplication No. PCT/JP2009/001541, filed Apr. 1, 2009, which designatedthe US and claims priority to Japanese Patent Application No.2008-095901, filed Apr. 2, 2008, the entire contents of each of whichare hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a synthetic resin-made thrust slidingbearing, and more particularly to a thrust sliding bearing which issuitably incorporated as a thrust sliding bearing of a strut-typesuspension (Macpherson type) in a four-wheeled motor vehicle.

BACKGROUND ART

Particularly in Patent Document 1, a sliding bearing is proposed whichis comprised of an upper casing formed of a synthetic resin and having avehicle body-side seat surface for a vehicle body side and an annularlower surface; a lower casing which is formed of a synthetic resin, issuperposed on the upper casing so as to be rotatable about the axis ofthe upper casing, and has an annular upper surface opposed to theannular lower surface of the upper casing; and an annular thrust slidingbearing piece which is formed of a synthetic resin, and is interposedbetween the annular lower surface and the annular upper surface, whereina spring seat surface for a suspension coil spring is integrally formedon a portion of the lower casing on an outer peripheral side of thevehicle body-side seat surface and the thrust sliding bearing piece.According to such a sliding bearing, since the spring seat surface forthe suspension coil spring is provided on the lower surface, it ispossible to dispense with a spring seat member made of sheet metal.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP-A-2004-293589

SUMMARY OF THE INVENTION

Problems that the Invention is to Solve

Incidentally, with such a sliding bearing, since the spring seat surfaceis formed on the portion of the lower casing on the outer peripheralside of the vehicle body-side seat surface and the thrust slidingbearing piece, when the vehicle body load is supported, there is apossibility that deflection is likely to occur in such as the lowersurface where the spring seat surface is integrally formed.

The present invention has been devised in view of the above-describedaspects, and its object is to provide a thrust sliding bearing which iscapable of reducing the possibility that deflection is likely to occurwhen the vehicle body load is supported.

Means for Overcoming the Problems

A thrust sliding bearing in accordance with the invention includes: asynthetic resin-made upper casing which has a vehicle body-side seatsurface for a vehicle body side and an annular lower surface; asynthetic resin-made lower casing on which an annular upper surfaceopposed to the annular lower surface and a spring seat surface for asuspension coil spring are integrally formed, and which is superposed onsaid upper casing so as to be rotatable about an axis of said uppercasing; and a thrust sliding bearing piece which is disposed in anannular gap between the annular lower surface and the annular uppersurface, and has an annular thrust sliding bearing surface whichslidably abuts against at least one of the annular lower surface and theannular upper surface, wherein the vehicle body-side seat surface, thethrust sliding bearing surface, and the spring seat surface are arrangedby being juxtaposed to each other in an axial direction.

According to the thrust sliding bearing in accordance with theinvention, since, in particular, the vehicle body-side seat surface, thethrust sliding bearing surface, and the spring seat surface are arrangedby being juxtaposed to each other in the axial direction, it is possibleto reduce the possibility that deflection is likely to occur in such asthe lower casing where the spring seat surface is integrally formed whenthe vehicle body load is supported.

In a preferred example of the thrust sliding bearing in accordance withthe invention, a portion of the spring seat surface where the suspensioncoil spring abuts, the vehicle body-side seat surface, and the thrustsliding bearing surface are arranged in series to each other in theaxial direction. According to such a preferred example, it is possibleto further reduce the possibility that the deflection is likely tooccur.

In another preferred example of the thrust sliding bearing in accordancewith the invention, said thrust sliding bearing piece has the annularthrust sliding bearing surface which slidably abuts against the annularlower surface, and said lower casing has a plurality of recessedportions or hole portions formed in the annular upper surface. Accordingto such a preferred example, deformations such as expansion andshrinkage based on thermal change at the time of injection molding ofthe synthetic resin-made lower casing can be allowed to take placelocally at the aforementioned plurality of recessed portions or holeportions. Hence, it is possible to prevent a decline in the fabricationaccuracy of the lower casing on which the spring seat surface isintegrally formed, particularly a decline in the fabrication accuracy ofthe annular upper surface of the lower casing.

In still another preferred example of the thrust sliding bearing inaccordance with the invention, the plurality of recessed portions orhole portions are arranged at equal intervals in a circumferentialdirection.

In a further preferred example of the thrust sliding bearing inaccordance with the invention, said lower casing includes an annularbase portion having the annular upper surface formed thereon and acylindrical portion formed integrally on a lower portion of the annularbase portion, the spring seat surface is formed by an outer peripheralsurface of the cylindrical portion and a lower surface of the annularbase portion, and a portion formed by the lower surface of the annularbase portion of the spring seat surface where the suspension coil springabuts, the vehicle body-side seat surface, and the thrust slidingbearing surface are arranged in series to each other in the axialdirection. According to such a preferred example, it is possible tofurther reduce the possibility that the deflection is likely to occur.

In a still further preferred example of the thrust sliding bearing inaccordance with the invention, said upper casing includes an annularbase portion having the vehicle body-side seat surface formed on itsupper surface and the annular lower surface formed on its lower surface,and an outer cylindrical suspended portion which is suspended from anouter peripheral portion of the annular base portion toward a side ofsaid lower casing, and an inside diameter of the outer cylindricalsuspended portion at its end portion on the lower casing side isgradually enlarged as a position of the inner peripheral surface of theend portion is located gradually away from the annular base portion inthe axial direction. According to such a preferred example, it ispossible to suitably prevent the ingress of muddy water from the endportion on the lower casing side of the outer cylindrical suspendedportion between the upper casing and the lower casing.

In a further preferred example of the thrust sliding bearing inaccordance with the invention, a portion of an outer peripheral surfaceof said lower casing opposed to the end portion of the outer cylindricalsuspended portion on the lower casing side is located gradually awayfrom the end portion as the position of the outer peripheral surface ofsaid lower casing is located away from the annular base portion of saidupper casing.

In a further preferred example of the thrust sliding bearing inaccordance with the invention, an annular engaging hook portion having ashape of a recessed surface for engaging said lower casing is formed onan inner peripheral surface of the outer cylindrical suspended portion,and the engaging hook portion is adjacent to the end portion of theouter cylindrical suspended portion on the lower casing side.

The thrust sliding bearing in accordance with the invention ispreferably used as a thrust sliding bearing of a strut-type suspensionin a four-wheeled motor vehicle.

In the thrust sliding bearing in accordance with the invention, theupper casing and the thrust sliding bearing piece may be formed of asynthetic resin. In such a case, the synthetic resin for forming theupper casing and the lower casing may be a thermoplastic synthetic resinsuch as polyacetal resin, polyamide resin, or polyester resin. Inaddition, the synthetic resin for forming the thrust sliding bearingpiece may be a thermoplastic synthetic resin such as polyacetal resin,polyamide resin, polyolefin resin, or polyester resin.

Advantages of the Invention

According to the invention, it is possible to provide a thrust slidingbearing which is capable of reducing the possibility that deflection islikely to occur when the vehicle body load is supported.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory cross-sectional view of an embodiment of theinvention;

FIG. 2 is an explanatory plan view of the embodiment shown in FIG. 1;

FIG. 3 is an explanatory fragmentary view of the thrust sliding bearingof the embodiment shown in FIG. 1;

FIG. 4 is an explanatory perspective view of a lower casing of theembodiment shown in FIG. 1;

FIG. 5 is an explanatory plan view of the lower casing shown in FIG. 4;

FIG. 6 is an explanatory cross-sectional view taken along line V-V inthe direction of arrows shown in FIG. 4;

FIG. 7 is an explanatory cross-sectional view of an upper casing of theembodiment shown in FIG. 1;

FIG. 8 is a partially enlarged explanatory cross-sectional view of theupper casing shown in FIG. 7;

FIG. 9 is a partially enlarged explanatory cross-sectional view of thethrust sliding bearing of the embodiment shown in FIG. 1;

FIG. 10 is a partially enlarged explanatory cross-sectional view ofanother embodiment of the invention; and

FIG. 11 is a partially enlarged explanatory cross-sectional view ofstill another embodiment of the invention.

MODE FOR CARRYING OUT THE INVENTION

Hereafter, a more detailed description will be given of the presentinvention on the basis of the preferred embodiments illustrated in thedrawings. It should be noted that the present invention is not limitedto these embodiments.

In FIGS. 1 to 9, a thrust sliding bearing 1 in accordance with thisembodiment for use as a strut-type suspension in a four-wheeled motorvehicle is comprised of an annular upper casing 3 which is formed of asynthetic resin such as polyacetal resin and has a vehicle body-sideseat surface 10 for a mounting member 8 on the vehicle body side and anannular lower surface 2; an annular lower casing 5 which is formed of areinforced synthetic resin including a synthetic resin such aspolyacetal resin and reinforcing fibers such as glass fibers containedin this polyacetal resin, on which an annular upper surface 4 opposed tothe annular lower surface 2 and a spring seat surface 25 for asuspension coil spring 7 are integrally formed, and which is superposedon the upper casing 3 so as to be rotatable about an axis O of the uppercasing 3 in an R direction; and an annular thrust sliding bearing piece6 which is formed of a synthetic resin such as polyacetal resin, isdisposed in an annular gap 9 between the annular lower surface 2 and theannular upper surface 4, and has an annular thrust sliding bearingsurface 51 which slidably abuts against at least one of the annularlower surface 2 and the annular upper surface 4, i.e., the annular lowersurface 2 in this embodiment.

The upper casing 3 includes a circular ring-shaped base portion 11having the vehicle body-side seat surface 10 formed on its upper surfaceand the annular lower surface 2 formed on its lower surface; an outercylindrical suspended portion 12 which is suspended from an outerperipheral portion of the circular ring-shaped base portion 11 towardthe lower casing 5 side; and an inner cylindrical suspended portion 13which is suspended from an inner peripheral portion of the circularring-shaped base portion 11 toward the lower casing 5 side. The outercylindrical suspended portion 12 and the inner cylindrical suspendedportion 13 are integrally formed on the circular ring-shaped baseportion 11. The annular lower surface 2 is formed by the lower surfaceof the circular ring-shaped base portion 11 between the outercylindrical suspended portion 12 and the inner cylindrical suspendedportion 13.

An annular projection 15 projecting toward the lower casing 5 is formedon a portion of the lower surface of the circular ring-shaped baseportion 11 which is on the side of the outer cylindrical suspendedportion 12. An annular recessed groove 16 which is recessed with respectto the lower casing 5 is formed on the lower surface of the innercylindrical suspended portion 13. An annular engaging hook portion 17 isformed on the inner peripheral surface of the outer cylindricalsuspended portion 12.

An upper surface 18 of the circular ring-shaped base portion 11 and aninner peripheral surface 19 of the inner cylindrical suspended portion13 abut against the mounting member 8, as shown, for example, in FIG. 1.

The lower casing 5 includes a circular ring-shaped base portion 21having the annular upper surface 4 formed on its upper surface; acylindrical portion 22 formed integrally on a lower portion of the innerperiphery of the circular ring-shaped base portion 21 in such a manneras to be suspended from the circular ring-shaped base portion 21; thespring seat surface 25 for a suspension coil spring which is integrallyformed by an outer peripheral surface 23 of the cylindrical portion 22and an annular lower surface 24 of the circular ring-shaped base portion21; and a plurality of recessed portions or hole portions, i.e., aplurality of recessed portions 26 in this embodiment, which are formedin the annular upper surface 4 and arranged at equal intervals in thecircumferential direction.

An annular engaged hook portion 27 is integrally formed on the outerperipheral surface of the circular ring-shaped base portion 21. Theengaging hook portion 17 has the shape of a recessed surface, while theengaged hook portion 27 has the shape of a protruding surfacecomplementary to the shape of the recessed surface. When the uppercasing 3 is superposed on the lower casing 5, the engaging hook portion17 is restorably deflected while being brought into sliding contact withthe engaged hook portion 27, and is engaged with that engaged hookportion 27.

An annular projection 28 projecting toward the upper casing 3 isintegrally formed on a portion of the upper surface of the circularring-shaped base portion 21 which is on the side of the engaged hookportion 27. An annular recessed groove 29 which is recessed with respectto the upper casing 3 is formed between the engaged hook portion 27 andthe annular projection 28. The annular projection 15 is disposed in suchan annular recessed groove 29.

An annular projection 30 projecting toward the upper casing 3 isintegrally formed on the upper surface of the cylindrical portion 22,and such an annular projection 30 is disposed in the annular recessedgroove 16. A plurality of ribs 31 which are arranged at equal intervalsin the circumferential direction are provided at a connecting portionbetween the upper surface of the cylindrical portion 22 and the innerperipheral surface of the circular ring-shaped base portion 21. Itshould be noted that the lower casing 5 may have recessed portions 45each formed between the plurality of ribs 31, as shown in FIG. 6.

The annular projection 15 and the annular recessed groove 29 form alabyrinth structure on the outer peripheral side of the thrust slidingbearing piece 6, and the annular recessed groove 16 and the annularprojection 30 form a labyrinth structure on the inner peripheral side ofthe thrust sliding bearing piece 6. These labyrinth structures preventthe ingress of foreign objects such as dust into the annular gap 9.

The inner peripheral surface 19 of the inner cylindrical suspendedportion 13 and an inner peripheral surface 32 of the cylindrical portion22 define a through hole 35 having the axis O as its center. The vehiclebody-side seat surface 10, the thrust sliding bearing surface 51, andthe spring seat surface 25 are arranged by being juxtaposed to eachother in the axial direction of the thrust sliding bearing 1. Thatportion of the spring seat surface 25 where the suspension coil spring 7abuts, i.e., in this embodiment the portion formed by the lower surface24 of the circular ring-shaped base portion 21 of the spring seatsurface 25 where the suspension coil spring 7 abuts, the vehiclebody-side seat surface 10, and the thrust sliding bearing surface 51 arearranged in series to each other in the axial direction.

The inside diameter of the outer cylindrical suspended portion 12 at itsend portion 61 on the lower casing 5 side is gradually enlarged as theposition of the inner peripheral surface of the end portion 61 islocated gradually away from the circular ring-shaped base portion 11 inthe axial direction. The engaging hook portion 17 which is locatedcloser to the circular ring-shaped base portion 11 side than the endportion 61 is contiguous to the end portion 61. The inner peripheralsurface of the end portion 61 is inclined so as to come gradually closerto the outer peripheral side of that end portion 61 as the position ofthe inner peripheral surface of the end portion 61 is located graduallyaway from the circular ring-shaped base portion 11. The portion of theouter peripheral surface of the circular ring-shaped base portion 21opposed to such an end portion 61 is located gradually away from the endportion 61 as the position of the outer peripheral surface of thecircular ring-shaped base portion 21 is located gradually away from thecircular ring-shaped base portion 11. Since the thrust sliding bearing 1has such an end portion 61 of the outer cylindrical suspended portion12, it is possible to suitably prevent the ingress of muddy water fromthat end portion 61 between the upper casing 3 and the lower casing 5.

It should be noted that an open end 62 which is defined by the endportion 61 and the portion of the outer peripheral surface of thecircular ring-shaped base portion 21 opposed to that end portion 61 isoriented toward the spring seat surface 25 in this embodiment, but thisopen end 62 may be oriented toward the outer peripheral side of thethrust sliding bearing 1 by adopting instead of the lower casing 5 alower casing 65 in which the shape of the portion of the outerperipheral surface of the circular ring-shaped base portion 21 opposedto the end portion 61 is curved toward the outer peripheral side, asshown in FIG. 10.

The plurality of recessed portions 26 are constituted by a plurality ofrecessed portions 41 having the shape of a triangle in a plan view andarranged at equal intervals in the circumferential direction and aplurality of recessed portions 42 having the shape of an inversetriangle in a plan view and respectively located between adjacent onesof the plurality of recessed portions 41. Each of the recessed portions41 and 42 gradually expands from a bottom surface 43 toward an opening44. The depth of each of the recessed portions 41 and 42 is abouttwo-thirds of the thickness of the circular ring-shaped base portion 21.

Such a lower casing 5 is molded as a raw material is injected into amold from a plurality of gates arranged at equal intervals in thecircumferential direction and located in correspondence with each of theinner peripheral surface 32 and a lower surface 33 of the cylindricalportion 22. Since the lower casing 5 has the plurality of recessedportions 26, even if the lower casing 5 undergoes thermal deformationand the like at the time of injection molding, such deformation can beallowed to take place locally at those recessed portions 26. Moreover,since the recessed portions 26 are formed on the annular upper surface4, it is possible to maintain high fabrication accuracy of the annularupper surface 4, in particular.

The thrust sliding bearing piece 6 has an annular plate body 52 with thethrust sliding bearing surfaces 51 formed on its upper and lowersurfaces and a cylindrical portion 54 which is integrally formed on theinner peripheral portion of the annular plate body 52 in such a manneras to extend toward the lower casing 3 side, and has radial slidingbearing surfaces 53 formed on its inner peripheral surface and outerperipheral surface. The surface roughness in the circumferentialdirection of the thrust sliding bearing surfaces 51 and the radialsliding bearing surfaces 53 is 1 μm or less, preferably 0.5 μm or lessand more preferably 0.1 μm or less. It should be noted that the surfaceroughness of the annular lower surface 2, the annular upper surface 4,the outer peripheral surface of the inner cylindrical suspended portion13, and the inner peripheral surface of the circular ring-shaped baseportion 21 preferably is equal to or less than the surface roughness ofthe thrust sliding bearing surfaces 51 and the radial sliding bearingsurfaces 53.

The annular plate body 52 has an outside diameter smaller than theinside diameter of the annular projection 28, and the cylindricalportion 54 has an inside diameter greater than the outside diameter ofthe inner cylindrical suspended portion 13 and an outside diametersmaller than the inside diameter of the circular ring-shaped baseportion 21. The thrust sliding bearing piece 6 is disposed in theannular gap 9 between the annular lower surface 2 and the annular uppersurface 4, between the outer peripheral surface of the inner cylindricalsuspended portion 13 and the inner peripheral surface of the circularring-shaped base portion 21, and between the annular projections 28 and30, slidably abuts at each of the thrust sliding bearing surfaces 51against each of the annular lower surface 2 and the annular uppersurface 4, and slidably abuts at each of the radial sliding bearingsurfaces 53 against each of the outer peripheral surface of the innercylindrical suspended portion 13 and the inner peripheral surface of thecircular ring-shaped base portion 21.

It should be noted that grooves for lubricating oil, in which alubricant oil such as grease is filled, may be formed on the uppersurface of the annular plate body 52 of the thrust sliding bearing piece6 and on the inner peripheral surface of the cylindrical portion 54thereof. Such grooves for lubricating oil may be constituted by such asan annular groove and a plurality of radial grooves extending radiallyfrom this annular groove.

According to the thrust sliding bearing 1 in accordance with thisembodiment, the thrust sliding bearing 1 is comprised of the syntheticresin-made upper casing 3 which has the vehicle body-side seat surface10 for the vehicle body side and the annular lower surface 2; thesynthetic resin-made lower casing 5 on which the annular upper surface 4opposed to the annular lower surface 2 and the spring seat surface 25for the suspension coil spring 7 are integrally formed, and which issuperposed on the upper casing 3 so as to be rotatable about the axis Oof the upper casing 3 in the R direction; and the thrust sliding bearingpiece 6 which is disposed in the annular gap 9 between the annular lowersurface 2 and the annular upper surface 4, and has the annular thrustsliding bearing surface 51 which slidably abuts against at least one ofthe annular lower surface 2 and the annular upper surface 4. Since thevehicle body-side seat surface 10, the thrust sliding bearing surface51, and the spring seat surface 25 are arranged by being juxtaposed toeach other in the axial direction, it is possible to reduce thepossibility that deflection is likely to occur in such as the lowercasing 5 where the spring seat surface 25 is integrally formed when thevehicle body load is supported.

According to the thrust sliding bearing 1, that portion of the springseat surface 25 where the suspension coil spring 7 abuts, the vehiclebody-side seat surface 10, and the thrust sliding bearing surface 51 arearranged in series to each other in the axial direction, it is possibleto further reduce the possibility that the deflection is likely tooccur.

According to the thrust sliding bearing 1, the thrust sliding bearingpiece 6 has the annular thrust sliding bearing surface 51 which slidablyabuts against the annular lower surface 2, and the lower casing 5 hasthe plurality of recessed portions 26 serving as the plurality ofrecessed portions or hole portions formed in the annular upper surface4. Therefore, deformations such as expansion and shrinkage based onthermal change at the time of injection molding of the syntheticresin-made lower casing 5 can be allowed to take place locally at theaforementioned plurality of recessed portions 26. Hence, it is possibleto prevent a decline in the fabrication accuracy of the lower casing 5on which the spring seat surface 25 is integrally formed particularly adecline in the fabrication accuracy of the annular upper surface 4 ofthe lower casing 5.

According to the thrust sliding bearing 1, the lower casing 5 includesthe circular ring-shaped base portion 21 having the annular uppersurface 4 formed thereon and the cylindrical portion 22 formedintegrally on the lower portion of the circular ring-shaped base portion21. The spring seat surface 25 is formed by the outer peripheral surface23 of the cylindrical portion 22 and the lower surface 24 of thecircular ring-shaped base portion 21. That portion formed by the lowersurface 24 of the circular ring-shaped base portion 21 of the springseat surface 25 where the suspension coil spring 7 abuts, the vehiclebody-side seat surface 10, and the thrust sliding bearing surface 51 arearranged in series to each other in the axial direction. Therefore, itis possible to further reduce the possibility that the deflection islikely to occur.

According to the thrust sliding bearing 1, the upper casing 3 includesthe circular ring-shaped base portion 11 having the vehicle body-sideseat surface 10 formed on its upper surface and the annular lowersurface 2 formed on its lower surface, as well as the outer cylindricalsuspended portion 12 which is suspended from the outer peripheralportion of the circular ring-shaped base portion 11 toward the lowercasing 5 side. The inside diameter of the outer cylindrical suspendedportion 12 at its end portion 61 on the lower casing 5 side is graduallyenlarged as the position of the inner peripheral surface of the endportion 61 is located gradually away from the circular ring-shaped baseportion 11 in the axial direction. Therefore, it is possible to suitablyprevent the ingress of muddy water from the end portion 61 of the outercylindrical suspended portion 12 between the upper casing 3 and thelower casing 5.

Although in the above-described embodiment the outer cylindricalsuspended portion 12 has the end portion 61 with an inside diameterwhich is gradually enlarged as the position of the inner peripheralsurface of the end portion 61 is located gradually away from thecircular ring-shaped base portion 11 in the axial direction, the outercylindrical suspended portion 12 may alternatively be formed so as toterminate at the end portion where the engaging hook portion 17 isformed, by omitting the end portion 61, as shown in FIG. 11. In thiscase, the open end 62 which is defined by the engaging hook portion 17and a portion of the outer peripheral surface of the circularring-shaped base portion 21 opposed to that engaging hook portion 17 isopen toward the spring seat surface 25.

1. A thrust sliding bearing comprising: a synthetic resin-made uppercasing which has a vehicle body-side seat surface for a vehicle bodyside and an annular lower surface; a synthetic resin-made lower casingon which an annular upper surface opposed to the annular lower surfaceand a spring seat surface for a suspension coil spring are integrallyformed, and which is superposed on said upper casing so as to berotatable about an axis of said upper casing; and a thrust slidingbearing piece which is disposed in an annular gap between the annularlower surface and the annular upper surface, and has an annular thrustsliding bearing surface which slidably abuts against at least one of theannular lower surface and the annular upper surface, wherein the vehiclebody-side seat surface, the thrust sliding bearing surface, and thespring seat surface are arranged by being juxtaposed to each other in anaxial direction.
 2. The thrust sliding bearing according to claim 1,wherein a portion of the spring seat surface where the suspension coilspring abuts, the vehicle body-side seat surface, and the thrust slidingbearing surface are arranged in series to each other in the axialdirection.
 3. The thrust sliding bearing according to claim 1, whereinsaid thrust sliding bearing piece has the annular thrust sliding bearingsurface which slidably abuts against the annular lower surface, and saidlower casing has a plurality of recessed portions or hole portionsformed in the annular upper surface.
 4. The thrust sliding bearingaccording to claim 3, wherein the plurality of recessed portions or holeportions are arranged at equal intervals in a circumferential direction.5. The thrust sliding bearing according to claim 3, wherein said lowercasing includes an annular base portion having the annular upper surfaceformed thereon and a cylindrical portion formed integrally on a lowerportion of the annular base portion, the spring seat surface is formedby an outer peripheral surface of the cylindrical portion and a lowersurface of the annular base portion, and a portion formed by the lowersurface of the annular base portion of the spring seat surface where thesuspension coil spring abuts, the vehicle body-side seat surface, andthe thrust sliding bearing surface are arranged in series to each otherin the axial direction.
 6. The thrust sliding bearing according to claim1, wherein said upper casing includes an annular base portion having thevehicle body-side seat surface formed on its upper surface and theannular lower surface formed on its lower surface, and an outercylindrical suspended portion which is suspended from an outerperipheral portion of the annular base portion toward a side of saidlower casing, and an inside diameter of the outer cylindrical suspendedportion at its end portion on the lower casing side is graduallyenlarged as a position of the inner peripheral surface of the endportion is located gradually away from the annular base portion in theaxial direction.
 7. The thrust sliding bearing according to claim 6,wherein a portion of an outer peripheral surface of said lower casingopposed to the end portion of the outer cylindrical suspended portion onthe lower casing side is located gradually away from the end portion asthe position of the outer peripheral surface of said lower casing islocated away from the annular base portion of said upper casing.
 8. Thethrust sliding bearing according to claim 6, wherein an annular engaginghook portion having a shape of a recessed surface for engaging saidlower casing is formed on an inner peripheral surface of the outercylindrical suspended portion, and the engaging hook portion is adjacentto the end portion of the outer cylindrical suspended portion on thelower casing side.
 9. The thrust sliding bearing according to claim 1for use as a thrust sliding bearing of a strut-type suspension in afour-wheeled motor vehicle.